Contents

Technologies

Thermoacoustics

Other Acoustic Technologies

A Sound Way to Turn Heat into Electricity - University of Utah physicists developed small devices that turn heat into sound and then into electricity via piezoelectric conversion. The technology holds promise for changing waste heat into electricity, harnessing solar energy and cooling computers and radars. (PESN; May 5, 2007)

Los Alamos National Laboratory has developed an "Acoustic Stirling Heat Engine" with no moving parts. It converts heat into intense acoustic power. [1]

Acoustic Propulsion - Two spherical Helmholtz resonators (glass Christmas tree bulb ornaments with a resonance frequency of 386 Hz) connected by a thin rod and suspended from a thread will rotate when driven at their resonance frequency, provided that the driving sound is loud enough (in this case more than 125 dB). (Free Energy Blog; November 11, 2013)

Comments

Increased Efficiency Losses

To first convert heat to sound and then sound to electrical
energy will not yield over 12-15% efficiency, which is where we are with
peltier and Seebeck devices today.

Heat to sound is not simple or efficient, (20-30%) and sound to electric
(as in piezoelectric or capacitive (electret) microphones) is quite
mature, but not considered of good efficiency (25-35%). Other possible
choices like Barium titanate transducers might be a little better, but
still not dramatic.

To compound 2 low efficiency devices (20-30% each) will not yield over
10% final net efficiency.

This is not likely to beat existing techs.

Rebuttal

The Los Alamos National Laboratory team that
developed the first practical acoustic Stirling engine
now has its efficiency up to 30%. They say linear
motor/generators can be driven by this engine, and
such generators are over 80% efficient. 30% x 80% =
24%. A 90% alternator would make it 27%. These are
much better numbers than James Dunn claims they are.

I say thermoacoustic engines with linear alternators
are more efficient than common thermoelectric
generators. They are about the same in cutting edge
TEG designs which are reported to be about 25%
efficient.

For those of you who do not know, Peltier and Seebeck
devices are the same thing! They are thermoelectric
devices such as thermocouples, thermopiles, and
thermoelectric generators. The Peltier effect is the
phenomenon of heat-to-electricity and
electricity-to-heat at a thermoelectric junction, such
as a p-n junction in semiconducting materials; a solar
cell exhibits the same thing with a particular
wavelength of light. The Seebeck effect is the
voltage of said junction, as a function of
temperature, measured in volts per degree.